Automated shift transmissions for motor vehicles usually have a mechanically operating parking lock device in which a locking device is operated to reach the locking position. The locking device is, for example, a locking pawl which engages the teeth of a parking lock gear which is connected to the output of the transmission, and thus to an axle of the vehicle. Usually, the parking lock is engaged by a spring-type actuator whose spring tension moves an actuating element of the locking device in such a manner that the locking pawl is locked in the direction of its motion, and able to snap into engagement with the teeth of the parking lock gear. To disengage the parking lock, a release device is required that allows the parking lock to be released. Usually, the release device is operated by a drive, such a hydraulic drive, additionally provided for this. In the disengaged state, the parking lock can be held by a retaining device, such as a solenoid with a retaining mechanism. During this, the retaining device must provide a retention force counteracting the spring tension of the spring-type actuator.
The retaining device must be designed in such a manner the retention force of the retaining device is greater than the spring tension of the spring-type actuator. In order to provide the retention force, high power consumption is required, for example, for a solenoid. If the retaining device is operated by a solenoid, the parking lock remains in the disengaged state as long as the solenoid is energized. Using a solenoid in the retaining device ensures that, in the event of an electrical power failure, the retaining device is disengaged, allowing the parking lock to be engaged. In this connection, the problem may arise that the parking lock is engaged at a vehicle speed at which the transmission would be damaged. Therefore, engagement of the parking lock at a vehicle speed greater than a certain limit vehicle speed must be avoided. It is an object of the present invention to further develop a parking lock for an automated transmission of a motor vehicle of the type mentioned at the outset in such a manner that the parking lock can be engaged and disengaged in a reliable and simple manner.